Artificial photosynthesis and 'solar fuels' could be possible

Caltech
scientists, inspired by a chemical process found in leaves, have developed an
electrically conductive film that could help pave the way for devices capable
of harnessing sunlight to split water into hydrogen fuel. When applied to
semiconducting materials such as silicon, the nickel oxide film prevents rust
buildup and facilitates an important chemical process in the solar-driven
production of fuels such as methane or hydrogen.

George
L. Argyros Professor and Professor of Chemistry Nate Lewis and postdoc Ke Sun,
who together have helped develop a protective film that is rust-resistant,
highly transparent, and highly catalytic. This new thin-film could help pave
the way for devices capable of harnessing the sunlight to generate fuels.
Credit: Lance Hayashida/Caltech Marcomm

"We
have developed a new type of protective coating that enables a key process in
the solar-driven production of fuels to be performed with record efficiency,
stability, and effectiveness, and in a system that is intrinsically safe and
does not produce explosive mixtures of hydrogen and oxygen," says Nate
Lewis, the George L. Argyros Professor and professor of chemistry at Caltech
and a coauthor of a new study, published the week of March 9 in the online
issue of the Proceedings of the National Academy of Sciences (PNAS), that
describes the film.

The
development could help lead to safe, efficient artificial photosynthetic
systems—also called solar-fuel generators or "artificial leaves"—that
replicate the natural process of photosynthesis that plants use to convert
sunlight, water, and carbon dioxide into oxygen and fuel in the form of
carbohydrates, or sugars. The artificial leaf that Lewis' team is developing in
part at Caltech's Joint Center for Artificial Photosynthesis (JCAP) consists of
three main components: two electrodes—a photoanode and a photocathode—and a
membrane. The photoanode uses sunlight to oxidize water molecules to generate
oxygen gas, protons, and electrons, while the photocathode recombines the
protons and electrons to form hydrogen gas. The membrane, which is typically
made of plastic, keeps the two gases separate in order to eliminate any
possibility of an explosion, and lets the gas be collected under pressure to
safely push it into a pipeline.

Scientists
have tried building the electrodes out of common semiconductors such as silicon
or gallium arsenide—which absorb light and are also used in solar panels—but a
major problem is that these materials develop an oxide layer (that is, rust)
when exposed to water. "Our team is also working on a photocathode,"
Lewis says. "What we have to do is combine both of these elements together
and show that the entire system works. That will not be easy, but we now have
one of the missing key pieces that has eluded the field for the past
half-century." (Source: Phys.org)